Abstract : Digenean trematodes encompass several species with little morphological differentiation in the larval stages and, as a result, uncertainty prevails regarding species identification. The microphallid trematode Maritrema subdolum occurs widespread geographically in mud snail and crustacean hosts in European marine shallow-water ecosystems. Larval stages of this and other congeneric species are, however, difficult to separate morphologically. To verify the species status and to secure identification of two co-occurring microphallids, M. subdolum and microphallid sp. no. 15 (Deblock, 1980), we examined the nucleotide sequences of the internal transcribed spacer regions (ITS1, ITS2). From fragments consisting of both ITS regions and the 5.8S gene (nearly 1,200 bp), a sequence divergence of 2.9% between the two types was recorded. In accordance with the morphological traits of the cercariae (stylet shape, length), the results support the view that the two types actually represent different species. Species-specific primers were prepared for each species. They proved to be efficient diagnostic tools for identifying single larval-stage individuals. Using these primers, infections in host organisms were also verified without performing a dissection of the host individuals.